Metastasizing to the colon from triple-negative breast cancer: A case report and review of literature

Abstract

BACKGROUND

Breast cancer (BC) metastasis to the gastrointestinal tract is uncommon, colonic metastasis from BC (CMBC) is even rarer.

CASE SUMMARY

This report describes a 44-year-old female patient with metastatic triple-negative BC in the ascending colon who underwent laparoscopic radical right hemicolectomy. The patient had undergone left modified radical mastectomy only 15 months ago and stopped chemotherapy just 3 months ago. The diagnosis of CMBC was made based on the previous history of BC and positive results of several specific immunohistochemical markers (gross cystic disease fluid protein 15, mammaglobin, GATA-binding protein 3, and cytokeratin 7) for breast carcinoma.

CONCLUSION

CMBC should be highly cautious in patients with a previous history of BC, especially triple-negative BC, and further examination to aid in diagnosis.

Key Words: Breast cancer; Colon metastasis; Colonoscopy; Pathology; Surgery; Review; Case report

Core Tip: This report describes a 44-year-old female patient with metastatic ductal breast cancer (BC) in the ascending colon who underwent laparoscopic radical right hemicolectomy. Colonic metastasis from BC (CMBC) is extremely rare. The case is presented along with a literature review. The results of our study remaindered that CMBC should be highly cautious in patients with a previous history of breast carcinoma, especially triple negative BC. Attention should be paid to the gastrointestinal symptoms during follow-up for BC. A detailed examination including immunohistochemical analysis of endoscopic biopsies prior to surgery should be performed.

INTRODUCTION

Breast cancer (BC) is the most common malignancy among women, with nearly 2090000 new cases diagnosed each year[1]. Triple-negative BC (TNBC) accounts for 10%–20% of all cases. TNBC is a subtype of breast tumor, accounting for 10%–20% of all cases, and it lacks the expression of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER-2). Compared to hormone-sensitive subtypes, TNBC has a higher recurrence rate, an increased risk of visceral metastasis, and a poorer prognosis[2]. TNBC also tends to be more aggressive and difficult to diagnose by conventional imaging[3]. Though BC is the second leading cause of mortality in women, recent advancements in systemic treatments, such as surgical resection, chemotherapy, radiotherapy, and hormonal therapy, have remarkably improved its prognosis compared to other types of cancer[4]. Approximately 5%-10% of diagnosed BCs may metastasize, and at least 20%-50% of patients experience metastasis at some point during their lifetime[5]. The common sites for BC metastasis include the lungs, bones, liver, and brain, and metastasis of BC to the gastrointestinal (GI) tract is relatively rare[6]. In some cases of GI metastasis from BC, it predominantly affects the stomach or small intestine[7,8]. However, few cases of colonic metastasis from BC (CMBC) have been reported[9], let alone its pathology and effective treatment options.

To elucidate the potential progression of CMBC and develop effective therapeutic strategies for treating CMBC, we reported a case of a 44-year-old woman with colonic metastasis detected during screening colonoscopy, who underwent radical mastectomy for BC one year ago. This case report is expected to provide valuable insights into the treatment of CMBC and similar diseases.

CASE PRESENTATION

Chief complaints

A 44-year-old female patient was admitted to the Department of Gastroenterology at our hospital because of mild abdominal distension and intermittent abdominal dull pain in the right lower abdomen for one month.

History of present illness

The patient did not present with hematochezia, melena, changes in bowel habits, or any other concomitant symptoms. The patient did not complain of nausea, vomiting and fever. Also, she did not present any symptoms of obstruction such as stopped anal exhaust and defecation. However, the patient's body weight decreased by about 3 kg in the past three months.

History of past illness

The patient was admitted to the Department of Breast Surgery at our hospital in July 2020 due to enlarged cervical and axillary lymph nodes. Following diagnosis with TNBC, she received six cycles of preoperative neoadjuvant chemotherapy consisting of epirubicin, docetaxel, and cyclophosphamide until October 2020. According to clinical pathological staging, TNBC was classified as cT2N3M0 (stage IIIC)[10]. After chemotherapy, significant shrinkage was observed in both the breast mass and supraclavicular area, but no apparent reduction in the size of axillary lymph nodes was observed. In November 2020, under general anesthesia, a modified radical mastectomy procedure was performed on her left breast as a palliative radical treatment to suppress the metastasis of BC. Following the modified radical mastectomy, the patient received capecitabine maintenance therapy until November 2021. Radiotherapy to the left breast was completed from December 2020 to February 2021. The patient underwent regular follow-up examinations periodically from February to December 2021.

Personal and family history

The patient had no personal history and family history of cancer.

Physical examination upon admission

Abdominal examination revealed slight tenderness in the right lower abdomen.

Laboratory examinations

From February to December 2021, laboratory data showed that there were no elevation in the levels of carcinoembryonic antigen (CEA) and cancer antigen (CA) 19-9. In January 2022, the patient had a hemoglobin level of 124 g/L, a hematocrit level of 38.3%, a mean corpuscular volume level of 98.7 FL, an aspartate aminotransferase level of 27.9 U/L, an alanine transaminase level of 13.7 U/L, and an alkaline phosphatase level of 74.9 U/L. Moreover, the patient had a CA-153 level of 36.9 U/mL (reference range: 0-26.4 U/mL), a CA-125 level of 41.8 U/mL (reference range: 0-35 U/mL), and a CEA level of 7.88 U/mL (reference range: 0.0-5.2 ng/mL).

Imaging examinations

In July 2020, ultrasound (US) evaluation detected solid nodules measuring approximately 12 mm × 6 mm × 10 mm in the left breast, which was classified as Breast Imaging Reporting and Data System: 5, as well as metastatic involvement of the left supraclavicular and axillary lymph nodes. The patient received an US-guided puncture biopsy for left breast nodules and affected lymph nodes in the axilla and supraclavicular region. Pathological examination confirmed invasive carcinoma in the left breast nodules, as well as metastasis to axillary and supraclavicular lymph nodes. Immunohistochemical analysis showed negative results for HER-2, PR, and ER. However, the ki-67 index was found to be 20%. In November 2020, postoperative pathological examination of mastectomy confirmed invasive ductal carcinoma (IDC) without involvement of either the nipple or basal margins. Forty-five of 46 examined axillary lymph nodes were positive. The immunohistochemical staining of endoscopic biopsies demonstrated that this case was positive for GATA-binding protein 3 (GATA-3), gross cystic disease fluid protein 15 (GCDFP-15), E-cadherin, S-100, and cytokeratin (CK) 7, and ki-67 (10%), but negative for PR, ER, HER-2, and CK14. A positron-emission tomography scan conducted in June 2021 revealed no evidence of metastasis in the GI tract and other parts of the body (Figure 1). In January 2022, only 15 months after the modified radical mastectomy, colonoscopy unveiled a fragile mass measuring approximately 4 cm × 5 cm in size within the ascending colon that occupied the entire intestinal lumen (Figure 2). Furthermore, multiple small polyps were detected during colonoscopy in the descending colon and rectum. The contrast-enhanced computed tomography (CT) scan confirmed that adenocarcinoma was present in the ascending colon (Figure 3), which was further verified by pathological examination of endoscopic biopsies (Figure 4). Postoperative immunohistochemical staining of the resected ascending colon specimen showed that the tumor was positive for GCDFP15, GATA3, mammaglobin, E-cadherin, CK7, CK20, and CEA; and the ki-67 index was 50%. However, ER and PR were negative (Figure 5).

Figure 1 18F-fluorodeoxyglucose positron emission tomography/computed tomography. 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography images didn’t reveal high uptake of FDG in the gastrointestinal tract and other parts of the body in June 2021.

Figure 2 Colonoscopy showing a brittle mass in the ascending colon measuring about 4 cm × 5 cm in size. The mass occupied the entire intestinal lumen. The lumen was narrow, and the colonoscope could not pass through it.

Figure 3 Contrast-enhanced computed tomography. It showing the wall thickening of the ascending colon with a significantly enhanced soft tissue density mass causing an apparent stenosis (arrow).

Figure 4 Colon biopsy. It showing the diagnosis of poorly differentiated adenocarcinoma in the ascending colon.

Figure 5 Immunohistochemical staining of colon specimens. A: Gross cystic disease fluid protein 15; B: GATA-binding protein 3; C: Mammaglobin; D: Cytokeratin 7. Tumor cells were positive.

FINAL DIAGNOSIS

We examined the excised BC specimen and found that it had striking pathological similarities with the resected ascending colon specimen. As mentioned above, the BC specimen was negative for PR, ER, and HER-2. Interestingly, both breast and colon specimens were positive for GCDFP-15, GATA-3, and CK7 (Figure 6). Taken together, these results confirmed colonic metastasis from TNBC.

Figure 6 Immunohistochemical staining of breast cancer specimens. A: Gross cystic disease fluid protein 15; B: GATA-binding protein 3; C: Cytokeratin 7. Tumor cells were positive.

TREATMENT

In July 2020, following diagnosis with TNBC, we first selected consisting of epirubicin, docetaxel, and cyclophosphamide other than endocrine to perform preoperative chemotherapy. Until October 2020, after 6 cycles, the tumor was found to be significantly reduced, while the axillary metastatic lymph nodes were not significantly reduced. In November 2020, under general anesthesia, a modified radical mastectomy procedure was performed on her left breast as a palliative radical treatment to suppress the metastasis of BC. Following the modified radical mastectomy, in view of resistance to anthracyclines, capecitabine chemotherapy was chosen until November 2021. Unfortunately, capecitabine was stopped after 4 cycles because of hand-foot syndrome. Radiotherapy to the left breast was completed from December 2020 to February 2021. In January 2022, only 15 months after modified radical mastectomy, the patient underwent laparoscopic radical right hemicolectomy for right colon cancer.

OUTCOME AND FOLLOW-UP

The patient experienced an uneventful postoperative course, with a satisfactory recovery, and was discharged 11 days after surgery. One month later after discharge, the follow-up examination revealed that the levels of postoperative tumor markers were elevated, with CA-15-3 increasing from 36.9 U/mL to 52.4 U/mL and CA 125 from 41.8 U/mL to 58.6 U/mL. Therefore, chemotherapy was recommenced utilizing albumin-bound paclitaxel and carboplatin. Table 1 shows the timeline of the patient’s clinical history.

Table 1 The timeline of the patient’s clinical history.

Timeline	Diagnosis and treatment process	Result
July 2020	Ultrasound-guided puncture biopsy and pathological examination	Diagnosed with triple-negative breast cancer
Until October 2020	Six cycles of preoperative neoadjuvant chemotherapy	Significant shrinkage of the breast mass and supraclavicular area; no apparent reduction in size for the axillary lymph nodes
November 2020	A modified radical mastectomy procedure	Postoperative pathology: Invasive ductal carcinoma, 45 of 46 examined axillary lymph nodes (+), gross cystic disease fluid protein 15 (+), GATA-binding protein 3 (+), E-cadherin (+), CK7 (+), S-100 (+), and ki-67 (10%); estrogen receptor, human epidermal growth factor receptor 2 (-), progesterone receptor (-) and CK14 (-)
November 2020 to November 2021	Chemotherapy consisting of capecitabine and radiotherapy	CEA 4.3 ng/mL and CA 19-9 25.1 U/mL
February 2021 to December 2021	Follow-up	No observed elevation in CEA and CA 19-9 tumor markers, and no evidence of metastatic disease with positron emission tomography/CT
February 2022	Colonoscopy, laboratory investigations, CT scan and biopsy outcomes	A comprehensive preoperative diagnosis with ascending colon cancer
February 2022	Laparoscopic radical right hemicolectomy, morphological and immunohistochemical examination	Diagnosed with colonic metastasis from breast cancer

CA: Cancer antigen; CEA: Carcinoembryonic antigen; CK: Cytokeratin; CT: Computed tomography.

DISCUSSION

The histologic type of CMBC

BC is the most prevalent cancer among women under 50 years of age, accounting for 24% of newly diagnosed cases[11]. GI metastasis from BC is relatively rare, occurring in about 3.4%-4.5% of patients[12,13]. In comparison, CMBC is even rarer. A retrospective study conducted by McLemore et al[14] identified only 24 cases of CMBC out of 12001 BC patients between 1985 and 2000. IDC is the most common invasive BC. Borst and Ingold[15] reported that among 2605 cases of metastatic BC (MBC), including 359 Lobular carcinomas and 2246 ductal carcinomas, only a small proportion (4.7%) have metastasized to the GI. GI metastasis from BC is predominantly associated with invasive lobular carcinoma, while IDC has been reported in limited studies[16]. In this case, the histologic type of primary BC was also IDC.

By using the combined terms "Breast Cancer/carcinoma" with "Colonic Metastasis", "colon cancer", and "sigmoid" in PubMed, we obtained only 22 case reports of CMBC (Table 2)[9,17-38]. Among these reports, there was an interval of 2 years or more between the resection of BC and the surgical resection of CMBC. However, our present case is unique as it involves a patient with both IDC and advanced-stage (stage IIIC) TNBC. Consequently, the patient was treated with adjuvant systemic therapy. Despite this treatment, colonic metastasis occurred just 15 months after mastectomy and merely 3 months following chemotherapy cessation. To make matters worse, positron emission tomography (PET)/CT scans during close follow-up did not reveal any clear pathological findings; yet, 8 months later, an impending obstructive colonic lesion was discovered. Based on the available literature, our case recorded the shortest interval of time between surgical resection of BC and colonic metastasis.

Table 2 Summary of reported cases of colonic metastasis from breast cancer.

Ref.	Age	Original diagnosis (triple-negative breast cancer, Y/N)	Time since mastectomy (years)	Adjuvant treatment after mastectomy	Preoperative symptoms	Colonic metastasis detection by positron emission tomography/computed tomography (Y/N)	Preoperative diagnosis of colonic metastasis from breast cancer (Y/N)
Kamitani et al[17], 1987	56	ILC (N)	7	ND	Abdominal pain	ND	N
Babb and Trollope[18], 2001	72	ND (N)	18	Radiotherapy; hormonal therapy	Asymptomafic	ND	N
Vaidya et al[19], 2002	56	IDC (ND)	5	Radiotherapy; hormonal therapy	Change in bowel habit and weight loss	ND	Y
Zhou et al[20], 2012	54	IDC (N)	6	Chemotherapy; radiotherapy; hormonal therapy	Asymptomafic	ND	Y
Maekawa et al[21], 2012	54	IDC (N)	16	Chemotherapy; hormonal therapy	Asymptomafic	Y	Y
Nikkar-Esfahani et al[22], 2013	63	ILC (ND)	17	ND	Mild abdominal distension	ND	N
Motos-Micó et al[23], 2014	69	ILC (ND)	18	Chemotherapy	Abdominal pain, nausea, vomiting	ND	N
Kim and Moon[24], 2015	46	ND	2	Chemotherapy; radiotherapy	Intermittent hematochezia	Y	Y
Andriola et al[25], 2015	63	IDC and ILC (N)	23	Chemotherapy	A moderate abdominal pain	Y	Y
Gizzi et al[26], 2015	72	ILC (N)	11	Chemotherapy; radiotherapy; hormonal therapy	Abdominal pain and diarrhoea	Y	Y
Jeong et al[27], 2016	58	Inflammatory breast cancer (N)	4	Chemotherapy	Obstructive symptoms	N	Y
Aihara et al[28], 2017	64	ND (ND)	ND	ND	ND	ND	Y
Tsujimura et al[29], 2017	51	ILC (N)	ND	ND	Abdominal pain, vomiting and diarrhea	Y	Y
Horimoto et al[30], 2018	47	IDC and ILC (N)	5	Chemotherapy; hormonal therapy	Asymptomatic	No	N
Falco et al[31], 2018	67	ILC (N)	14	Chemotherapy; hormonal therapy	Asymptomatic	Y	Y
Schellenberg et al[32], 2018	69	IDC (N)	5	Chemotherapy; radiotherapy; hormonal therapy	Asymptomatic	N	Y
Jones et al[33], 2019	55	IDC (N)	4	Hormonal therapy	Nausea, vomiting and abdominal pain	Y	N
Bering et al[34], 2020	67	ILC (N)	ND	Chemotherapy; hormonal therapy	Change in bowel habit	N	N
Sarfraz et al[35], 2020	60	ILC (N)	5	Hormonal therapy	Abdominal pain, distension, and vomiting	ND	Y
Higley et al[36], 2020	74	ILC (Y)	20	Radiotherapy; hormonal therapy	Decreased stool caliber and constipation	ND	N
Chen et al[37], 2021	62	ND (N)	9	ND	Abdominal pain, bloating	ND	N
Inoue et al[9], 2022	63	ILC (N)	15	Chemotherapy hormonal therapy	Asymptomatic	Y	N
Botto et al[38], 2023	59	ILC(N)	2	Chemotherapy; radiotherapy; hormonal therapy	Asymptomafic	N	Y
This case	44	IDC (Y)	1	Chemotherapy	Abdominal pain and distension	N	N

IDC: Invasive ductal carcinoma; ILC: Invasive lobular carcinoma; ND: Not described; N: No; Y: Yes.

Comprehensive diagnostic methods and multidisciplinary cooperation

CMBC often presents without symptoms or with non-specific symptoms. Based on our literature review, potential symptoms may include abdominal pain, diarrhea, bowel obstruction, or asymptom. If patients have a history of BC and new GI symptoms, consideration should be given to the possibility of CMBC[39]. In this particular case, the patient experienced mild abdominal distension and intermittent dull pain in the right lower abdomen for one month. It is challenging to clinically and radiologically differentiate CMBC from primary colon cancer. Radiographic imaging techniques such as conventional contrast-enhanced CT can aid in diagnosis. However, radiological features like nodular or circumferential thickening with narrowing can easily be mistaken for primary colonic tumors or inflammatory colonic diseases-similar to what occurred in this case. PET-CT is another commonly used radiological imaging method. According to the literature, PET-CT is not recommended for diagnosing primary BC due to its limited sensitivity in detecting small tumors (0–10 mm). However, it is suitable for detecting distant metastases with higher specificity and sensitivity relative to conventional imaging[40]. It has been reported that PET-CT exhibits a sensitivity of 80% to 100% and a specificity of 75% to 100%[41]. In this case, however, the PET-CT scan did not reveal a significant uptake of fluorodeoxyglucose in the ascending colon during follow-up. Only 8 months after the PET-CT scan, an impending obstructive colonic lesion was detected by colonoscopy in the patient. There could be two possible explanations for this situation. First, there might have been no tumor present at the time of the initial PET-CT scan, and the tumor might develop within eight months. Second, it is plausible that the tumor was too small to be detected by PET since PET had lower sensitivity towards metastatic masses. Nevertheless, there are also many cases where metastatic lesions are found by PET examination (Table 2). In addition to PET-CT, another important preoperative examination used in diagnosing CMBC is endoscopy biopsy. During endoscopic examinations, macroscopic appearance may appear normal which differs from primary colon cancer[42]. The pathological findings may show necrotic tissues and no carcinoma due to technical limitations in identifying tumors[42]. Therefore, obtaining multiple deeper biopsies penetrating the serous side of the colon is crucial for accurately diagnosing metastatic breast carcinoma. In our case, colonoscopy revealed a brittle mass and intestinal lumen stenosis in the ascending colon, and it was difficult to distinguish between primary and metastatic lesions. The pathological biopsy also confirmed the diagnosis of poorly differentiated adenocarcinoma in the ascending colon. Unfortunately, however, due to nonspecific symptoms and radiographic and endoscopic features resembling primary colon cancer, we were unable to make an accurate preoperative diagnosis. Although the accuracy of comprehensive multidisciplinary diagnostic methods is limited, cooperation between different departments should be enhanced to integrate more information and improve their diagnostic approaches to ensure timely and accurate identification of such metastases.

Immunohistochemical examination is crucial for the diagnosis of CMBC

When pathologists have difficulty in histological diagnosis, they should take into account the history of BC and immunohistochemical indicators of BC-related indicators. In challenging cases, immunohistochemistry may be the only diagnostic tool for accurately diagnosing CMBC. The breast-specific markers commonly used for tumors with unknown primary origins include GCDFP-15, mammaglobin, GATA-3, and CK7[43,44]. As a glycoprotein originally identified in human breast gross cyst fluids, GCDFP-15 has been widely used as a marker for apocrine differentiation due to its relatively high specificity and sensitivity[45]. Around 20% of patients with MBC show high GCDFP-15 levels in plasma[46], and 50% or higher of cases express GCDFP-15[47]. Another study shows that immunohistochemical analysis of mammaglobin is superior to GCDFP-15 in identifying tumors of breast origin. Mammaglobin is positive in a about 84% of MBCs are positive for mammaglobin[48]. Mammaglobin is highly expressed in primary BCs, however, it exists at low levels in healthy breast tissues and has not been detected in non-breast tumors and other tissues, suggesting that it is suitable for diagnosing BC[49-51]. GATA-3 is another effective marker for detecting BC metastasis, and its expression in metastatic lesions shows high concordance with that in primary lesions[52,53]. Positive staining for CK7 (+) suggests that the primary site of metastases may be the breast, however, CK7 is usually negative in colorectal cancer[54]. Because these markers are neither fully specific nor sensitive, recognizing the clinical context and tumor location, along with the specific markers for other organs, is key to accurate diagnosis[55]. In our case, immunohistochemistry showed that excised right colon cancer specimens were positive for GCDFP-15, GATA-3, mammaglobin, and CK7, which are similar to the results of resected BC specimens. Hence, a diagnosis of CMBC was made.

The mechanisms and pathways in CMBC

The progression of TNBC is poorly understood, which may involve epigenetic and genetic alterations, intravasation through the basement membrane, extravasation into distal tissues, survival in the circulation, angiogenesis, and tumor-stroma interactions[56]. Cancer metastasis is closely associated with genetic instability of primary tumor cells, immune invasion, and the surrounding microenvironment. Surgical interventions or chemotherapeutic treatments are often ineffective against dormant cells that can reactivate and rapidly form new tumors. As one of the major cytoskeletal components, actin is involved in almost all steps of metastatic spread. Efforts have been made to find ways to treat cancer by interfering with actin and its regulatory factors. For example, low-frequency rotating magnetic fields can hinder BC metastasis by disrupting F-actin[57]. In addition, the epithelial-mesenchymal transition, angiogenesis, cell migration, and anoikis resistance are important factors in the metastatic progression of cancer cells. lncRNA-related orphan receptor (ROR) is a non-coding RNA, and it can inhibit p53 translation by directly interacting with the heterogeneous ribonuclear protein I. The primary function of mlncRNA-ROR is to maintain embryonic stem cells through induced pluripotent stem cells, and it can also play a role in carcinogenesis. It’s reported that receptor-ROR functions as a competitive endogenous RNA for miR205 in human breast epithelial cells, thereby affecting epithelial-mesenchymal transition[58]. TNBC contains high levels of ROR, which affects miR145 and its target adenosine diphosphate ribosylation factor 6, possibly leading to BC invasion and metastasis. However, because CMBC cases are reported as individual cases, it is difficult to conduct large-scale systematic studies to decipher the specific mechanism of CMBC.

Treatment and prognosis

Many factors can affect the treatment of MBC, such as patient age, tumor burden, tumor characteristics, hormone receptor status, previous treatments, metastatic sites, and tumor-related symptoms. The conventional treatments for MBC include chemotherapy, radiation therapy, surgery, hormonal therapy, and immunotherapy. Recently, targeted therapy and gene therapy have also been developed in treating MBC. In addition, some new methods for modern cancer treatment can provide a promising strategy. Several new herbal compounds have been reported to improve chemotherapy, hormonal therapy and gene therapy in cancer treatment[58]. Other studies have also enhanced anti-tumor effects through improved delivery methods, such as nanotechnology combined with sustained release patterns to address drug solubility and low bioavailability[59]. Photodynamic therapy and ferroptosis have mutually reinforcing effects with high anti-tumor efficacy and safety. Cen et al[60] prepared thermally responsive nanoparticles by combining the ultraminiature palladium ruthenium alloy and Ru(II) with thermally responsive phase change materials and co-encapsulating them with polypyridyl-complex.

Generally, following the initial surgical treatment, combining multiple types of treatment is recommended. Surgery can resect the primary tumor, thereby reducing tumor burden and improving overall survival. Radiotherapy is often used after surgery, however, it is preferred to be combined with other treatments because of high resistance when tumor sizes are larger than 1 cm[61]. For MBC patients who have symptomatic or hormone receptor-negative disease (i.e., resistant to endocrine therapy), chemotherapy is considered the first treatment option. Anthracyclines (like epirubicin) are commonly used antibiotics in treating MBC, and they perform anti-tumor functions through various mechanisms[62]. The common combinations of anthracyclines include cyclophosphamide 5-fluorouracil plus epirubicin or doxorubicin or doxorubicin/epirubicin plus cyclophosphamide. Capecitabine is used in patients who are resistant to anthracyclines and taxanes[63]. Capecitabine is a new generation of fluorouracil-based compounds used in cancer therapy. In cells, thymidine phosphorylase can convert capecitabine to 5-fluorouracil. Because the activity of thymidine phosphorylase is significantly higher in tumor tissues than in normal tissues, capecitabine has higher activity in tumors, especially in the hypoxic regions that are resistant to chemotherapy, with relatively lower toxicity[64]. Several studies have confirmed the efficacy of capecitabine maintenance chemotherapy for patients with MBC, but the incidence of hand-foot syndrome and GI adverse reactions is high[65-67].

The prognosis of TNBC is relatively poor, and the patients cannot receive endocrine therapy or HER-2-targeted therapy. In our case, we first selected the combined regimen of TEC to perform preoperative chemotherapy. After 6 cycles, the tumor size was significantly reduced, while the axillary metastatic lymph nodes showed no significant reduction. Therefore, given the resistance to anthracyclines, capecitabine was used after mastectomy. Unfortunately, capecitabine was stopped after 4 cycles because of hand-foot syndrome. In our case, the patient presented with a single lesion localized to the ascending colon, so surgery is the best option.

In recent years, the survival of BC has substantially improved. However, the prognosis is still poor for GI metastasis from BC, and the average survival time from detecting GI metastases is about 1 year[68]. Prognosis is affected by the characteristics of primary tumors, such as their grade and size, lymph node status, and the levels of ER, PR and HER-2. Recently, several specific genes and proteins associated with BC have been identified, but they are less useful in predicting the prognosis of metastatic cancers because they are more related to primary tumors, rather than distant metastases[69,70]. Combining multiple factors has a more significant prognostic value than individual factors.

Based on these discussions above and the changing characteristics of our patient, this patient's clinical course is aligned with typical prognostic expectations.

CONCLUSION

This case of CMBC indicates that clinicians and researchers should be highly cautious when treating patients with late-stage MBCs, particularly TNBC, even at an unusual site like the colon. Especially, when patients also present with GI symptoms, along with the possible recurrence of the tumor indicated by laboratory tests and imaging examination, it is necessary to conduct an endoscopic examination for any suspicious lesions and perform immunohistochemical examinations of the biopsies. Additionally, pathologists should take into account the history of BC and immunohistochemical analysis of BC-related indicators. We suggest that future endoscopists focus on the mucosal manifestations of CMBC and increase their experience in this area. Additionally, models of CMBC can be established to study the pathways and mechanisms of metastasis, providing theoretical support for future research.